An aramid fiber may be classified into a para-aramid fiber and a metha-aramid fiber, wherein the para-aramid fiber is made in such a structure that benzene rings are linearly connected through an amide group (CONH). At this time, a strength of para-aramid fiber having a thickness of 5 mm is such as to lift up and maintain a two-ton car. Thus, the para-aramid fiber is used in various fields for advanced technology of aerospace industry as well as the industry for developing a bullet-resistant material.
A process for making an aromatic polyamide fiber commonly known as the aramid fiber includes steps of preparing an aromatic polyamide by polymerizing aromatic diamine with aromatic diacid chloride in a polymerization solvent containing N-methyl-2-pyrrolidone (NMP); preparing a spinning dope by dissolving the aromatic polyamide in a concentrated sulfuric acid solution; and preparing a filament by spinning the spinning dope using a spinneret and a coagulation bath.
This aramid fiber has a skin-core structure wherein the modulus in a surface layer of the aramid fiber is higher than the modulus in a core of the aramid fiber. That is, if a stress is applied to the aramid fiber, the stress is concentrated on the surface layer of the aramid fiber. Accordingly, a physical property in the surface layer of the aramid fiber is the most important component in determining the strength of the aramid fiber.
However, a related art method of preparing the aramid fiber can not realize a high strength of the aramid fiber since it is performed without consideration of the surface layer of the aramid fiber.